1 / 6

Overview of Some Chemistry in Natural Waters

Overview of Some Chemistry in Natural Waters. Gases dissolve according to Henry’s law: K H =[X(aq)]/P X ; X=O 2 , CO 2 , H 2 S, SO 2 , etc.  Oxidation-Reduction, Acid-Base, Anaerobic digestion. According to pH, can get leaching (dissolution) of various species from soil or rock.

tabithat
Download Presentation

Overview of Some Chemistry in Natural Waters

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Overview of Some Chemistry in Natural Waters Gases dissolve according to Henry’s law: KH=[X(aq)]/PX; X=O2, CO2, H2S, SO2, etc.  Oxidation-Reduction, Acid-Base, Anaerobic digestion According to pH, can get leaching (dissolution) of various species from soil or rock.

  2. Dissolved Oxygen: At 25°C, Henry’s law gives 8.7 mg/l, or 8.7 ppm. Note: This is small, changes greatly with temperature; thermal pollution can lower it significantly. In acid: O2 + 4H+ + 4e- 2 H2O In base: O2 + 2 H2O + 4e- 4OH- General example for oxidation of organics: CnH2nOm + kO2 nCO2 + nH2O Measure of organic content in water: Biochemical Oxygen Demand (BOD) (Microbial action) Chemical Oxygen Demand (COD)(Na2Cr2O7/ H2SO4) Total Organic Carbon (Typ. ~1 mg/l, 1 ppm C, in ground water) Dissolved Organic Carbon (Typ. ~5 ppm in surface waters)

  3. The pE scale: Analogous to pH; measure of extent to which waters are reducing in nature. pE=-log[e-]effective, i.e. -log of the activity of e-. Low pE=strongly reducing (more e-s available) High pE=weakly reducing (fewer e-s available)

  4. Alkalinity: A measure of the actual concentration of the basic anions in solution as carbonate. total alkalinity = 2[CO32-]+[HCO3-]+[OH-]-[H+] For total alkalinity, the titration is done to Methyl Orange endpoint, pH = 4. For Carbonate only (i.e., no HCO3-), the titration is done to the phenolphthalein endpoint, pH = 8 to 9 -- “phenolphthalein alkalinity.”

  5. Hardness: Measures the total concentration of Ca2+ and Mg2+ ions. Titrate with ethylenediaminetetraacetic acid (EDTA) Find the total number of moles of Ca2+ and Mg2+ ions, then convert to mass per liter of CaCO3 that would have the same number of ions. For example, if [Ca2+]+[Mg2+]=0.0010 M then, since m.w. CaCO3 = 100 g/mol, the hardness value is 0.001  100 = 100 mg /l.

More Related